The present invention relates to X, Y plotters and, more particularly, to an X, Y plotter combining both cut paper and strip paper operation in one device and, additionally, incorporating vacuum columns for strip paper loops which are oriented at right angles to one another.
X, Y plotters are well known in the art. In early versions, a rectangle of cut paper was placed on a flat surface and a pen was moved over the surface by a pair of motors responsive to X and Y signals, respectively. One motor was connected to drive a pen block holding the pen along a first track and the second motor was connected to drive the first track along a second track set at right angles to the first track.
Such flat-surfaced X, Y plotters took up a lot of square footage of space (horizontally or vertically, depending on the table's orientation) for the table holding the paper where the capability for large drawings was required. Accordingly, drum or roller plotters incorporating a technique generally as shown in FIG. 1 were developed. In a drum or roller plotter, such as that generally indicated as 10, a horizontal track 12 and a driving roller 14 are mounted to a pair of side members 16 in parallel relationship. A pen block 18 holding a pen 20 is mounted on the track 12 for horizontal movement in the direction of the arrow 22. Pen block 18 is moved by a first motor 24 driven in response to one of the X, Y signals and connected to the pen block 18 by metal tape drive 26, or the like. The driving roller 14 is journal-mounted for rotation and is driven in the direction of arrows 28 by a second motor 30 in response to the other signal of the X, Y pair. The drivin9 roller 14 is positioned with respect to the pen block 18 such that the pen 20 is in contact with the surface of the driving roller 14. The driving roller 14 is further provided with a pair of rows of sprocket projections 32 adjacent respective ends of the roller 14 adapted to co-act with holes 34 in strip paper 36 disposed over the roller 14. Thus, as the driving roller 14 and pen block 18 are moved in response to the X, Y signals, the desired X, Y plot 38 is created on the strip paper 36.
To provide for an extended length of strip paper 36 and the rapid movement and reversal of direction thereof without breaking caused by sudden tensile forces, the arrangement of FIG. 2 (which is substantially identical to a technique employed with magnetic tape drive units) is employed. This technique is shown in FIG. 2. FIG. 2 is an end view of apparatus similar to that of FIG. 1 which was shown in a front elevation. The driving roller 14 is disposed between a pair of supply/takeup rollers 40. Between each supply/takeup roller 40 and the driving roller 14, a vacuum column 42 is disposed which is connected to a source of vacuum, generally indicated as 44. In operation, the paper strip, as indicated by the dotted line 36, extends from one supply/takeup roller 40 over an idler roller 46, forms a loop 48 within one vacuum column 42, passes over the driving roller 14, forms a second loop 48 in the other vacuum column 42, passes over a second idler roller 46, and onto the other supply/takeup roller 40. Appropriate means (not shown) are provided for maintaining the length of the loop 48 in each vacuum column 42 by sensing its position and using the position to control the vacuum source 44. As a consequence, sudden relative movement between the supply/takeup rollers 40 and the driving roller 14 are buffered by the loops 48 and tensile loads on the strip paper 36 are virtually eliminated.
Turning now to FIG. 3, a prior art apparatus is shown in simplified side elevation employing the technique of the apparatus of FIG. 1 to the plotting of cut paper drawings. The plotter 50 of FIG. 3 comprises a base 52 supporting a driving roller 14, horizontal track 12, and pen block 18 substantially identical to those of the plotter 10 of FIG. 1. An idler roller 54, however, is added in parallel spaced relationship to the driving roller 14 and an endless belt 56 of Mylar, or the like, containing holes for gripping by the sprocket projections 32 of the driving roller 14 is disposed about the driving roller 14 and idler roller 54 such that the endless belt 56 moves in combination with the driving roller 14. Cut paper, as indicated by the dotted line 58, is temporarily secured to the surface of the endless belt 56 with drafting tape or the like. Thus, as the endless belt 56 moves beneath the pen 20, the cut paper 58 is moved in combination with it.
As can be seen from the drawings of FIGS. 1-3 taken with the descriptions thereof hereinbefore, each of the two basic types of plotters (strip paper and cut paper) has its advantages. To secure the advantages of both according to the prior art, however, two separate plotters are required. Because of the vacuum columns 42 required for proper operation of the strip drive apparatus of FIG. 2, it is not feasible or practical to combine the two plotters of FIGS. 2 and 3 even though such a combination would be desirable and would provide many benefits.
Wherefore, it is the object of the present invention to provide a dual-mode X, Y plotter having the capability of using both strip paper and cut paper and incorporating vacuum column buffer loops in the strip paper drive train.